Video scrambling and unscrambling system



l `vIDEo SCRAMBLING AND UNSCRAMBLING SYSTEM Filed April 8. 1954 March24, 1959 A; D. HOFFMANN ETAL 5 Sheets-Sheet 1 IN VEN TORS .NGE

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March 24, 1959 A. D. HOFFMANN 'E1-AL 2,379,324

VIDEO SCRAMBLING AND UNSCRAMBLING SYSTEM Filed April' s. 1954 sAsheets-sheen 2 a' mmf/15+ maza vk/M575 March 24, 1959A IA. D. HOFFMANNETAL VIDEO SCRAMBLING AND UNSCRAMBLING SYSTEM Filed April a, 1954 V 3Sheets-Sheet 3 United States Patent O Calif., assig'nor'sn foInternational Telemeter Corporation, Los Angeles, Calif., a corporationof Delaware Application April 8, 1954, Serial No. 421,886 1o claims.(ci. 17a- 5.1)

This' invention relates generally to television systems and, moreparticularly, to improvements in methods of and apparatus for scramblinga television transmission, so that it is made intelligible only by areceiver equipped with suitable unscrambling apparatus.

The recent growth of the television industry and recent experience intelevision broadcasting indicates that the broadcasting of televisionentertainment cannot be carried forward on a profitable basis ifreliance is placed solely on advertising revenues for defraying thecosts of producing and transmitting such entertainment. These factorsdemonstrate the need for a television transmitting and receiving systemwhich allows each televiewer to be charged for the particular programreceived on the individual television receivers. Charging forentertainment in this fashion is analogous to the purchase of tickets atthe box ofiice of a theater or like place of entertainment, and thisanalogy has-led to recent adoption of the term box-office television todescribe television systems of this character.

A number of box-otiice television systems, alternatively known assubscription television systems, have already been described. In onesystem scrambled, or coded, e11- tertainment material is broadcast insuch form as to be unintelligible when received on an ordinarytelevision receiver. Authorized receiving stations are fitted with anunscrambling, or decoding, apparatus which is capable of renderingintelligible the otherwise unintelligible transmissions. This decodingor unscrambling apparatus is controlled by key signals transmitted tothe individual receiving stations over the commercial telephone systems,and acharge for supplying-the key or control signal is made, the keysignal beingsupplied by a telephone operator only uponv request thereforby the subscriber, and the charge being. made as an incident tosupplying such a key signal upon request.

One of the outstandin disadvantages of a box-oiiice television system ofthe character 'described above resides in the necessity: for using landlines extending in a network telephone type system from the televisiontransmitting station to each tions, and the necessity for using specialswitchboard equipment and operating personnel to stati such equipmentand make the necessary charges for supplying the key signal.

Another type of physical key or card box-oce television system utilizesa which takes the place of the land line used in the system describedabove. In the physical key or card type system', considerable diicultywould normally be encountered in eecting the distribution of the keys orcards to the many potential users of the system.

The disadvantages of the box-office television systems just mentionedare largely obviated in box-oliice television systems of the typesdescribed in an application filed on January 19, 1950,-by David L. Loewet al., Serial Number 139,358, now Patent-No'.V 2,769,023, for PrepaidEntertainment Distribution System and in another appliL of thetelevision receiving stat 2,879,324 Patented Mar. 24, 1959 ICC 2. cationby Robert E. Gottfried et al., filed May l0, 1951;-- Serial Number225,651, now Patent No. 2,769,026, for Improvement InPrcpaidEntertainment Distribution'4 System, both applications being assigned'to this assignee. The systems disclosed insaid copending applicationsutilize a coin collection means at each receiving-stationy and place theunscramblingapparatus under the control of the coincollection mechanism.obviates the necessity of employing land lines or physicalv keys forcontrolling the operation of the unscrambling apparatus; As'- in thesystems described in said copending=application's,the operation of the@scrambling-mechanism results from the deposit of the coins in the coincollectingapparatus:

An essential feature of any box-office television system istheprovision-of thecodingor scrambling apparatusat the transmittingstationand theprovsion' of eo-oper'ating decoding or unscram'blingapparatus at each of the re ceiving stations. Such apparatus formaintaining the secrecy of the programs until the necessarypricehas'been paid or the corresponding charge is made must so operateas to render the transmitting signals unintelligible when received on anordinary television-receiver not equipped with the decodingA orunscrambling apparatus. The scrambled signals must be'of such characteras to be capable ofv beingvrendered'itelligible by meansof relativelysimple apparatus to` be installed: at each of the receiving stations.Furthermore, the type of secrecy afforded by the system m'ustbesubstantially foolproof s'o as to malte substantially impossible theunauthorized reception ofthe programs without the payment of the' pricecharged for such entertainment. This latter requirement preferably ismet by periodically varying the conditions' of the'coding or scramblings"o as to require the unscranibling' ap'- paratus' at each of thetelevision receivers to-beresponsivel to a control exercised at thetransmitting station;v

The present system employed for transmitting animage on television is tosca'n an' object in interlacedfashion. Thus a complete picture frame,representative of an optical image at a certain instan is composed oftwoelds of consecutively scanned parallelV lines arranged so that the linesof one field fall between theI lines of another field.

In a patent to Mayle, bla-2,472,774, there is described a system foreffecting secrecy 'in-'television systems-where in a commutating tube isprovided for' generating-pulses of irregular amplitude which aresuperimposed upon' the sau/tooth deection voltage' which is applied as avertical deection voltage. This composite wave is thenapplied to thevertical deflection coils of the television-carriera. This has theeffect of transmittinga picture whereirithe interlace of the' horizontallines? isnot' in sequence' but is irregular, as determined by thedifferent p'ulse4 a'mplitudes. A similar system is provided at thereceiver to permit decoding.

The present invention also operates on the principle of providing anirregular sequence for horizontal' scanning of successive fields in atelevision system; The present invention, however, achieves this resultin'a new and useful manner and without the necessity foradding twowaveforms, one ofthem with irregular shape. The addition of irregularwaveforms requires careful attention to correct phase relation, which isdiicult to achieve in practice with a high degree of precision.Furthermore, the present invention is directed'A to a television picturescrambling andunscrambling system which is particularly suitablel foruse with boroce television systems of the' type'described'in theaforementioned applications.

It is an object of the present invention to provide a novel anduseful-video scrambling and unscrambligap'- paratus and system suitablefor use in a' subscriber tele vision system.

It is still another object of the present invention to provide animproved video scrambling and unscrambling apparatus and system whichpermits simple alterations of the scrambling and unscrambling apparatusto change their operation sequence pattern, -thereby preserving secrecy.

It is a further object of the present invention to provide aninexpensive video scrambling and unscrambling apparatus for subscribertelevision use which enables preservation of secrecy.

' It is still a further object of the present invention to provide ascrambling system which scrambles the order of horizontal line groups,thereby'presenting an unintellig'ible picture.

Itis still another object of the present invention to provide a codingand decoding system which does not require extreme precision in theaddition of two waveforms.

Yet another object of the present invention is the provision of a codingand decoding system for television programs wherein all signals requiredare provided by the transmitted program signals without the use ofauxiliary channels for decoding signals.

The above objects, as well as other features of the invention, areachieved byfproviding a system wherein a group of pulses is provided tobe counted within the duration of a scanning ield. A counter countsthese different pulse groups, and its output, which is unique for eachcount, is used to channel vertical deection signals, each of which hasan amplitude representative vof a different one of said unique counts,the order of these deliection signals being determined by the order ofthe predetermined counts.

The features of the invention which are believed to be new are set forthwith particularity in the appended claims. The invention itself,however, together with further objects and advantages thereof, may bebest understood by reference to the following description, when taken inconjunction with the accompanying drawings, in which:

Figure 1 is a schematic diagram of an embodiment of the invention whichis used at a television transmitter for scrambling purposes;

Figure 2 is a detailed circuit of a commutating tube which isused forscrambling and unscrambling a program, respectively, at the transmitterand receiver; Figures 3A and 3B are wave shapes of the pedestal andvertical deection voltages obtained by using the -syst'emy describedherein;

Figure 4 insta schematic diagram' of lthe embodiment of theinvention-employed at a receiver for decoding purposes; f

Figure 5 is a circuit diagram of a binary counter stage employed in thisinvention;

Figure 6 is a circuit diagram of a binary register stage employed inthis invention; I

Figure 7 is a circuit diagram of a transfer gate employed in thisinvention;

Figure 8 is a circuit diagram of a current generator employed in thisinvention; and

Figure 9 is a schematic diagram of a receiver moditication to show theutility of the invention in a subscription television system.

As briey described previously, the system used in transmissionoftelevision pictures is to scan the object with a number of lines ineach tieldand to interlace the lines to present a frame. Thus, if thelines in the rst field were to be numbered l, 3, 5, 7, the lines in thesecond field would have the numbers 2, 4, 6, 8, and, due to the natureof the phosphor on a television tube and persistence of vision, theobserver would see a picture composed of lines 1, 2, 3, 4, If, forexample, one were to transmit in order line 1, then line 5, line 9, line7, and then, in the second eld, transmit lines in the sequence 2, 6, 8,4, a type of scrambling would be obtained. This occurs since a receivernot equipped with unscrambling apparatus would present these lines inthe sequence in which they are received in positions normally occupiedby lines l, 2, 3, 4, and thus a type of scrambled picture is eiectuated.A receiver with the unscrambling equipment wouldreceive these lines andpresent them properly positioned on the television tube so that anintelligible picture is seen. y

In an application for a Video Scrambling and Unscrambling System byLouis N. Ridenour, Serial Number 421,924, led April 8, 1954, there isdescribed a system for scrambling a transmitted video picture byemploying a digital counter to rearrange the sequence of transmission ofthe horizontal lines of the picture. A receiver employs a digitalcounter to permit the generation of vertical deflection voltages so thathorizontal lines appear on the receiver picture tube in the samesequence as they are transmitted. The invention herein also employs adigital counter but in a different manner and with different apparatusin order to vrearrange the sequence of transmission of groups vof linesat the transmitter to scramble the picture transmitted. The receiver hassubstantially similar apparatus which generates vertical detiectionvoltages so that the groups of lines are generated in the same sequenceas they are transmitted.

In rendering a television picture unintelligible using coding, as theamount of scrambling is increased the picture becomes more and moreunintelligible.y However, there is a level of scrambling beyond whichfurther scrambling does not make the picture any more unintelligible asfar as the viewer is concerned. This, in effect, is a subjective pointof diminishing returns, since further scrambling, although it succeedsin breaking up the tine structure of the picture still further,does notcontribute anything to picture confusion as far as the viewer isconcerned. vThe present invention takes advantage of this 'effect andthus achieves a subjective maximum of picture unintelligibility with aminimum of apparatus. By permutating line groups in space on the face ofa cathoderay tube (or, identically, in time of their transmission overthe television channel), the present invention achieves a saving indriving power over that which is required when individual linescrambling is used. There is also a saving in television terminalequipment, and the information handling capacity required of the codetransmission channel is'considerably reduced. There is a way of reducingthe'detlection power required when an individual line-scrambling'technique is used. This may be achieved by trading power for time,allowing lon'ger retrace intervals. However, for'any given number oflines per frame, this method of saving driving power would result inappreciable loss of active scanning time, with corresponding loss ofotherwise available'picture resolution.

It should be noted further that 'splitting a frame into six parts, forexample, and transmitting the horizontal lines of the six groups inorder within each group, but with the six groups themselves in randomorder, provides an adequately scrambled picture. If there are 525 linesper frame, then allowance to each group is 87%: lines. Allowing 51,6lines forgroup retrace, a total of 492 active lines remain in thepicture, which compares favorably with present practice, yet permitstransmission of a group synchronization pulse of sufticient energy todistinguish it easily from the horizontal synchronization pulses.

Reference is now made to Figure l wherein a schematic diagram of thepresent invention is shown. In Figure 1 there is shown only so much of atelevision transmitter which differs from the television transmitters asthey are presently known as is required to understand and reproduce thisinvention. This is done in order to preserve simplicity in the drawingsand explanation. However, from the explanation and drawings, it isbelieved that the interconnections required in order to incorporate thepresent embodiment of the invention with the standardasf-resertelevision transmitter' will ne readily as skilled in theartl.'i

A horizontal sync scilllt 10'0'15 thtiell-kowntype, which provides afrequency of 15,750 cyles'l per l second 1x1 accordance with thepresently established stand# ards, has tsoutput appliedto (l)a'fconiposite video mixed to providehorizontal blanking (not shown);-(-2) ahorizontal' sweep driver 12- (also wellknown) whence horizontaldetection currents are applied to the? carriera yokesand (3) a-divideby175 frequency'di'vider 14 and then to a multiply by 2 frequencymultiplier" 16 to provide 180 pulses per secondto'synchr'nizetheutput-of a-vertical sync generato'r 18:

The: vertical sync generator 18 will be hereafter referred to as thegroup sync generator. The output of the group sync generator is appliedto (l) f- 180-'cycleper-second sweep generator- 20;A (2) a; compositevideo mixer (not shown) to providevertical bla-nkingi-pulsesg (3)' a.'-one-milliseco'nd delayl line"42;. (4)v afrequency multiplierZ 4`4'whichmultiplies the output by't'hee to provide S40-pulses per second; and (5)a phase'diser-im'inator 46. The pur'pose of the phase discriminato'rtogether` with a reactance tub'e frequency control 48' is' to provide aservo loop, as is well known, for stabilizingthe horizontal and verticalsync' frequencies. The reference frequency required in the loop may beprovided-'from the 60cycle three-phase power obtained fror'n publicutility mains' after half-wav`e recticton without filtering.

A magnetic drum is providedwhich hasf recorded thereon,in'w'ellknown-fashion; a series-:f equallyspaced pulses around theperiphery to provide i-timing track. It willbe appreciatedth'at' if a'niag'nctic transducer head 32 is used to convert these magneticpulsesinto electrical pulses the frequency of the occurrence-of-the'=electrcalpulses depends upon the speed of rotatidnfthedrur- 30. Accordingly, therotation of the magnetic drulr'l-nl'a'y be accurately controlled andAmaintained by" employing a phase discriminator 34, the-inputs" towhichconsist of pulses from the magnetic transducer 32 which ispositionedover the timing track andalso 'pulses fr'o'rii' thethree-times multiplier 24 of the output'fof the' group s'yre generator18. These pulses have their phasescompared by the phase discriminator34A and the differential output-is applied as an error voltage toan'iotor'con'tller 36 which controls a synchrodrive motor 38 which,A inturn, drives the drum- 30. Accordingly, the' speed of the drum is'synchronized with the' 540 pulses per second derivedfrom the groupsync-generator; The-'5140-puls'es per-second signal m'a'y b'ef referredto hereafter the group call timing'lsign'l.

Referring now againl to` the'- mag'netic druii, itis also provided withasig'ril trackarundits-peiiphery In'tl'l'e signal track there arerecorded; a't spaced-' intelif'als' six diiernt'- pulse groups.: By2-pl`llse group *'r'l'ea'-itY a nuriiber of pulses ifiseqii'nce. This-numberna-y' b'e-'different for' each p'uls' g'rup Another rilagn'eticu'tr-ansi duc-erV 4o is employed isralienne' pulsa' groups-fandapplythe'r'n a's electrical si'g'na'ls to the ir'iputi of a` binaryco''nter to be coutetil The' p'ulse' groupsrriy" referred to' hereafteras group-call signals. The gl'up-t call signals are also applied to akye'i- 42 t-le'ytheotput-faf20 kc.- os'eillator Accordingly,- the keyeroutptis'a 20 kc'.- wave4 l'eye'd ol and on in'- a'c'corda'rice'with-thezgroup callsignals. The keyer outputz appliedi to' tli'e FM modulator'4`6 of the transmitter. The 20 k'c keyedv wave is'then mix'ed with'th'e' televisiomaur'a'l proga'm to'- transmitted via the auraltransmitter' 48, diplexe't 50; and'ta'nsmittin'g antenna- 52 totelevision'r'e'c'eivlers.-

group' calli signals`i are' applied' front thee pickup transducer 40 toa' coincidence gat'ef'5'4 Also applied-as a'n input t`o this gate are'the group call tiniiilgs'ignalsl The' coincidence gatel 54 of the'intended als'o known as" an And gate and requires the simultaneouspresence' of both input signals before'` a'n outputs n'alde ialble Sucha'gate" rriay be'seer' described andsow' 6 in an' article' entitled'Diode' Coincidence and Mixing 1 Cir# cuits' in Digital Computers' byTung Chang Chen, page 511, in the May' 1950 IRE Proceedings. Theoutput-of this And gate is applied to the lirst stage of ai counterconsisting of three flip-flop circuits'. Between each ipop stage 56 inthe counter there is provided the same type of And gate 94 having-as oneinput the out# put of the preceding hip-flop and as the' other inputthe'group call timing signal. Aceordingly, tl1`e" grupcll signals areentered intothe' counter from the first'` Arid g'ate and-they are tiredby the groupeall tiilin'gfsignals.

The output ofeach tlipflo'p` 56 ofthe counter isiap'- plie'd to anassociated transfer gate-58- which iseiiiplyed t'o transfer the binarycount into a nip-flop register 60, in order that this count may bestatieised. Thesignal employed to permit the transfer gates totrians'fer the binary count from the respective nip-flops into the'`register is provided by the output-of the one-milliseeond delay network62 which has had applied thereto the-out put from the group syncgenerator. Thisdela'y ne't work output consists of delayed 180 pulsespci" second; Accordingly, the count of the pulses inaE group-isenteredinto the i'p-op counter timed bythe group call timing pulses which are540 per second. This count is-thcn transferred into the ip-op registertimed byv the-,group sync generator, which accordingly transfers-tliecountat a rate of 180 per second. Since there are siX pulsegroups on thedrum, each group is transferred into the register each 180th of a secondor all of the gr'oups in second. Also, the drum speed must be such as topr'o'vide' the six` groups every 1&0 of a second;

The output of the flip-flop register is applied to three currentgenerators 102 ofthe t'y'pe previously described. These can have theircurrents set in the relationship 1, 2, 4, so that the counts can provideeight diliere'nt currents, depending upon the ones' of the currentgenerator selected. The output of the current generators' is connectedin single-ended fashion across a summing resistor 64 through which B+ issupplied. The output taken at the summing resistor is applied to thedetlection plates of a commutator tube 66. This voltage may have thewave shape shown in Figure 3A which is shown for a field. Thiscommutator tube is of a type well known and will be found described in apatent to Goldmark, No. 2,250,479.

Reference is now made to Figure 2, which shows the details of thecircuitry for the commutator tube. The commutator tube consists of acathode-ray tube having at least a cathode 68, a deflection electrode70, and six targets 72, with a separate external lead from each target.An electron beam generated by the cathode is deected to a desired one ofthe targets by a deecting electrode. The output of the group sweepgenerator 30, which consists of sawtooth pulses occurring at alcyc1eper-sec ond rate, is applied through a condenser 74 and across aclamping diode 76 and a resistor 78 to a low-pass lter 80. The output ofthe low-pass filter 8l) is applied across a voltage divider resistor 82.This resistor 82 is connected back to a tap on resistor 78. Accordingly,across the resistor 82 there will be combined'DC. from the rectitier andlter plus A.C. from the tapped portion of resistor 73. Each of the sixplates of the commutator tube is connected to a different tap on thisvoltage'divider resistor. The cathode-ray beam of the commutator tube isdellected to different ones of the targets in accordance with thecurrent provided from the current generators. This detlection signal, ofcourse, is determined by the group call signal. The voltage on a targetdetermines the cathode current. Accordingly, the output from' thecommutator tube is taken through its cathode 68 and applied to a D.C.amplifier 86 whichamplilies thi's signal and thus provides a sweepcurrent of suflcient amplitude to be applied to the camera tube yoke asvertical dellectionsignals.

Described in more detail, the operation' of the cornrn'utator tube inthepresent instance is' as follows: The

rectifier low-pass filter permits only a direct current voltage to passthrough to the voltage divider resistor. However, it will be noted thatsome sawtooth voltage component is applied since the voltage divider isreturned to a tap on the input resistor to the low-pass filter.Therefore, the voltage at any tapping point of the voltage dividerresistor is the sum of these two components. The composite voltagesobtained here have a resultant wave shape as shown in Figure 3B. This isthe wave shape for the vertical deflection current for a eld.

The cathode-ray beam is held on each target for an interval of 180th ofa second. During this time the voltages on the divider tap to which thetarget is connected are summed and detected as a modulation of thecathode current of the commutator tube. Since every target is selectedat least once within a field, the entire field is covered.

Since the order of selecting the targets is a function of the group callsignal, a change of the group call signal recorded on the drum willreadily change the code. Thus a program scrambling system is providedwhich can be very simply changed to provide a new order of theinterposition of line groups whenever such new order is desired.

It should be pointed out that the voltage used to dellect the commutatortube needs to be established only approximately, and such a rough"deflection voltage is provided easily from the summing resistor 64. nthe other hand, the camera tube line group pedestal must be establishedwith very high precision relative to the group sweep peak-to-peakvoltage. This is accomplished by means of the commutator tube; its mainfunction is to quantize the pedestal voltages precisely relative to thegroup sweep voltage.

The group .call signal may be further characterized as consisting of sixpedestal numbers (each pedestal number corresponding to a differenttarget in the commutator tube). These pedestal numbers may be called upin any random sequence.

Referring to Figure 4, the system required at the receiver for decodingthe signals transmitted and coding as previously described is seen. Theusual integrating and differentiating networks 90, 92 in the receiverprovide separation of the horizontal and vertical sync signals. Thehorizontal sync generator 94 functions in wellknown fashion to drive thehorizontal sweep driver 96 and provide the horizontal deflection signalsfor the television tube. The vertical sync generator 98 provides 180pulses per second to (l) a group sweep generator 100; (2) a multiplier102 which multiplies the 180 pulses per second by three; and (3) aone-millisecond delay network 104.

The three-times multiplier 102 operates in well-known fashion to providea 540 pulse-per-second signal which is synchronized with and correspondsto the group call timing signal at the transmitterf Coincidence gates106, binary counter stages 108, transfer gates 110, register stages 112,and current generators 114 are identical with the structure shown at thetransmitter. The group call signal, however, is obtained from the signalreceived from the FM detector of the receiver (not shown) which isapplied first to the audio network of the receiver (not shown) andsecond to a high-pass filter 120, which eliminates the audio programmaterial, and then to a 20 kc. tuned amplifier 122. Then the output ofthis 20 kc. amplifier is applied to a C.W. detector 124, which detectsthe transmitted group call signals. These signals are applied to thefirst And gate 106 of the counter to be counted and synchronized by the540 cycle group call timing pulses.

The output of the one-millisecond delay network 104 is again used totransfer the count into the register. The current generators 114 convertthe register digital count to an analogue deflection voltage which isemployed to loperate a commutator tube 126 in the receiver. The

network coupling the sweep generator to the six commuttor tube targetsis identical with that at the transmitter. The output from the cathodeof the commutator tube is a deflection current such as may be seen bythe wave shape in Figure 3B. This is amplified by the sweep driver 128to provide the vertical deection currents for the television picturetube. Thus the operation of these circuits at the receiver is the sameas has been described for the transmitter.

It will be. appreciated that the system is synchronized with the systemat the transmitter. It will be appreciated further that the order ofselection of one of the six groups is identical with that selected atthe transmitter. It should be appreciated further that unless a receiverincludes the equipment shown, the picture received will be completelyunintelligible.

Figure 5 is a circuit diagram of a flip-flop which may be founddescribed, for example, on pages 595-597 of Radio Engineering by Terman,published by the Mc- Graw-Hill Book Company. The terminals of thetrigger circuit are labeled in accordance with the terminalidentications used in the schematic diagram in Figure 1. In view of thewell-known operation of this type of trigger circuit, a furtherdescription is deemed unnecessary.

Figure 6 is a circuit diagram of a flip-flop circuit which is suitablefor use as a stage in the binary register shown in Figure 1. Here againthere is shown another form of the two-tube trigger circuit which iswell known in the field. The output of each stage is applied to acathode follower 229, 230, and the outputs taken from each of thesecathode followers are applied to switch contacts in the switching device222 from which they are interconnectcd in any desired coding arrangementto the various currentgenerators. The operation of this trigger circuitis also too well known to merit further discussion and is also found inthe previous reference, as well as others. The input and outputterminals have applied thereto the same identification letters as areused in Figure 1, in order to facilitate the identification thereof.

Reference is now made to the circuit diagram of a transfer gate which isshown in Figure 7. The terminals of the circuit in Figure 7 have thesame reference numerals applied thereto as are shown in Figure l, tofacilitate the understanding thereof. The transfer gate consists of twodiodes 232, 232', one of which has its anode coupled to the S terminalof a register flip-flop, the other of which has its anode coupled to theR' terminal of thesame flip-flop stage. The cathodes of these two tubesare respectively coupled through individual resistors 234, 234' to the 1and 0 output terminals of a counter flip-flop stage and also throughindividual resistors 236, 236' to a source of negative voltage. Twocondensers 238, 238' are used to couple the cathodes of these diodes tothe source of horizontal sync pulses. Accordingly, if it is assumed thatthe 1 output of a flip-flop stage is high and the 0 output is low, whena horizontal sync pulse is applied to the cathodes of both diodes theyare simultaneously cut olf, but when the sync pulse terminates, theanodes of both diodes assume substantially the potentials at theircathodes. Therefore, the S terminal is made high if it is not alreadyhigh and the R' terminal is low. Thereby, the grids of the registerstage have potentials applied which transfer the register into the samecondition as the associated counter stage. In this manner, each time thecounter assumes a new count, this is transferred into the register atthe termina? tion of the pulse being counted.

Referring now to Figure 8, there may be seen a circuit diagram of thecurrent generator. This consists of two tubes 240, 240' having theircathodes connected together and through a current limiting resistor 242to a source of negative biasing potential. This current limitingresistor 242 has its value selected so that the binary relationships ofeach one of the current generators is pre served. I n other words, theresistor for the first current generator permits current tb'- ow' whentletutes' receive' the proper signals at theircontrol grids; whichcurrent corresponds' to the unit 1. The' next current generator has twotubes with a common cathoderesistorY which permits twice as much currentto ow, etc.

Figure 9 is a schematic diagram showing how the embodiment of theinvention may be inserted into the television receiver of a subscriber'to al subscription television systemso that both paid and free programsmay' be seen. Connections are brought from the integrator 130' of thereceiver to the unscr'ar'nblerdeflection circuits 250 which representthe embodiment' of the inventions-shown' in Figure 3. Connection isals'o made from the integrator to the usual vertical deflectioncircuits' 252'wl1'ichincludes all the necessary circuits in a receiverfor vertical deflection except the verticall sweep driver 128. This is'connected to the output of the vertical deection circuits through thenormally closed contacts-7254,l 256 of varelay 260. The output fromthe'unscrnibler deflection circuits is connected to the normally open relaycontact 258. The coil of the relay'260 is connected toa coin bo'x 262. Asuitablev coin box and its associated controlling circuitry may be founddescribed in the" applications by Loew et al. and Gottfried et al.referred'to previously. When the relay 260 isnot operated, thesubscribers receiver' can receive free' programs in' thef usual manner.If the receivei is tuned to' a'. channel over which'a program is to be'transmitted fori which prior payment is-re quired, by transmission ofsuitable s'ignals-Pthe coin box is actuated t'o show'the amount ofpa'yment'- required. If such payment' is not made, the' subsequentlyreceived picture is scrambled and unintelligible; Ifthedemandedpaymentis made' by depositing the requisite' amount of coins in the coinbox, the coin' box servesto actuate the relay, thus permitting theunscr'ambling' circuits to unscramble the picture being received. Upon'cessation'of the program the coin box is restored to its initialVposition, the relay ishrendered inoperative, and the receiver is againin eonditioi'to' receive fr'ee'piogia'r's.

Accordingly, there'liasbeerfdescribedand shown herein new and improvedsystems for `scrambling a transmitted television program and forunscrambling. it at the receiver. The systems shown herein permit, witha minmum of difliculty, a large number of scrambling codes and alsopermit the changing of such codes with a minimum of difiiculty.

We claim:

l. A scanning system for determining the sequence of scanning horizontallines in successive scanning fields of a television system comprisingfirst electron deflecting means for defining the horizontal component ofa scanning trace, second electron deflecting means for defining thevertical component of said scanning trace including a digital counter,means to generate different groups of pulses within the interval of ascanning field, means to apply said different groups of pulses to saidcounter in succession to be counted, said counter providing a difierentdigital manifestation for each different pulse group count, means togenerate deflection signals, and means responsive to said counter to estlish as vertical deflection signals different amplitude ranges of saiddeflection signals corresponding to different digital manifestations ofsaid counter.

2. A scanning system for determining the order of scanning horizontallines in successive scanning fields of a television system comprisingfirst electron deflecting means for defining the horizontal component ofa scanning trace, second electron deflecting means for defining thevertical component of said scanning trace including a digital counter,means to generate dierent groups of pulses within the interval of ascanning field, means to apply said different groups of pulses to saidcounter in succession to be counted, said counter providing a differentdigital manifestation for each dierent pulse group count, means togenerate deflection signals, a potential 10 divider having al pluralityof? tps; means-F to. apply' sala deflection signals to said potentialdividergandfswitcli means to select the deflection' signal output'v fromdifferent taps' of said voltage dividerv in' al sequence determined bythe4 different digital' manifestations ofsaidcounter.

3. A scanning system for determiningthe' sequence of scanning horizontallines in successive scanningI fields-of' a* television tubecomprising-first electron-deflectingmeans'- for defining thc-horizontalcomponent ofascanning-'traccis'e'cond electron deflecti'ng meansfor'de'finingztlielvertical component of said s'ennin'g. traceincluding' af' digital' counter, means to generate differentv .groupsof? pulses' within the interval of a' scanning field, means# t'o applysaid different groups of`puls'e's to said counter' in succes: sion to becounted', said counter providing a differentA digital manifestation foreach' different pulse group-count; means to generate deflection signals,af potential? divider: having a' plurality of'tap's, means to apply'said deection' signals to said potential divider, avcommuttin'gtubefliav# ing a cathode-ray4 beani and a plurality oftarget? elec# tr'odes, means" cou'plingeachl of saidt'a'r'g'etele'ctrodesto a different one of said potential divider taps', means forgenerating differentdeflection signals for saidcommutatl' ing tuberepresentative' o'f saiddifferent digit'al manifesta= tions'of saidcounter, means`-to a'pply said deflection siga nals' tosaidcommuta'ting' tube' to deflect itscathode4ay beam to its targetelectrodes' in a' sequencedetermined by the digital manifestation ofsaid counter, and'm'eans to' derive' vertical deflection signalsfromvsaid commutating tube whose amplitude is determined'by said sequence;

4. A scanning' system as recited in'l'claimi 3' wherein said means to`generate different' groups` ofpulses com prises magnetic recordingmeans, meansl to drive= said magnetic recording means at aisp'ee'dsynchronized with sa'id means' to generate deflection signals,- apattern of magnetically recorded pulses on saidmagnetic recording means'eacli representative of s'aid groups of pulses, and transducer means toread said magnetically recorded pulses.

5. A scanning' system as recited in claim' 3 wherein said counter4includes a plurality of binary'stages to which said pulse' groups are'applied to be counted, a binary register', gate means responsive to saidmeans' to generate deflection signals to transfer the count ofA saidcounter into said register, means to delay said transfer for apredetermined interval and saidmeans for generating different deflectionsignals for said commutative tube representative of said differentdigital manifestations of said counter includes a plurality of currentgenerators, and means coupling said current generators to said registerto provide a current responsive to the count entered therein.

6. The combination with a television transmitting system of a televisionpicture scrambling system comprising first electron deflecting means fordefining the horizontal component of a scanning trace, second electrondeflecting means for defining the vertical component of said scanningtrace including a digital counter, means to generate different groups ofpulses within the interval of a scanning field, means to apply saiddifferent groups of pulses to said counter in succession to be counted,said counter providing a different digital manifestation for eachdifferent pulse group count, means to generate deflection signals, apotential divider having a plurality of taps, means to apply saiddeflection signals to said potential divider, a commutatng tube having acathode-ray beam and a plurality of target electrodes, means couplingeach of said target electrodes to a different one of said potentialdivider taps, means for generating different deflection signals for saidcommutating tube representative of said different digital manifestationsof said counter, means to apply said deflection signals to saidcommutating tube to deflect its cathode-ray beam to its targetelectrodes in a sequence determined by the digital manifestation of saidcounter, and means to derive vertical deflection sig- 11 nale fromsaidcommutating tube whose amplitude is determined by said sequence.

I. 1-,The --combination with a television transmitting system includinga vertical and horizontal synchronizing pulse generator of a televisionpicture scrambling system comprising means to record a plurality ofgroups of pulses in a,.predetermined order, the number of said groupsbeing determined by the number of portions into which a televisionpicture is to be divided and the order of group recording is establishedto be determinative of the interlace of said portions, a counter, meanssynchronized by -said vertical synchronizing pulse generator to applysaid-groups to said counter to be counted in said order, means togenerate vertical deection voltages, a potential divider'having aplurality of taps, means to apply said vertical deection voltages tosaid potential divider, means to`select deection voltage output fromdiierent taps of said vvoltage divider in a sequence determined by thegroup pulsecount of said counter, and means to transmit said plurality,of groups in said predetermined order.

8. The combination with a television transmitting system asrecited inclaim 7.wherein said means to apply said vertical deflection voltagesincludes an input resistor and a low-pass filter, said low-pass lterhaving its input connected across a portion of said input resistor'andits output connected to said potential divider, and said verticaldeflection voltages are applied across said input resistor.

9. In a receiver having vertical synchronizing generating circuits foral subscription television systemv of the type-wherein a program forwhich payment is required has the-video portion scrambled by rearrangingthe order of groups of horizontal lines, means for unscrambling saidvideo portion comprising a pulse counter having a pluralityoffelectrondischarge tubes, different counts being manifested by conduction andnonconduction of all 'ofasaidtnbes in dilerent patterns, means to applyto saidl countergroups ofpulses to be counted within a scanning tield,and means to convert the different conduction and nonconduction patternsof the tubes of said counter to different amplitude vertical electronbeam deecting signals, the order of said different patterns determiningthe order of interlace, means rto establisha payment demand for saidprogram at said receiver, normally inoperative means to permitutilization of said vertical 'electron beam deecting signals, and meansresponsive to payment of said payment demand to'operate saidnormallylinoperative means to permit utilization of said verticalelectron beam deecting signals.

lt). In a subscription televisionvsystem including a televisiontransmitter having a vertical synchronizing signal generator and areceiver, means at transmitter for scrambling the video portion of aprogram for which payment of coin is required comprising a digitalcounter, means to generate different groups of pulses within theinterval of a video scanning field, means to apply said different groupsof pulses to said counter in succession to be counted, said counterproviding a diierent digital manifestation for each different pulsegroup count, means to generate deflection signals,ga potential dividerhaving a plurality of taps, means to apply said deflection signals tosaid potential divider, switch means to select the dellection signaloutputs from different taps of said voltage divider in a sequencedetermined by the different digital manifestations of said counter,means to transmit said diterent pulse groups and said verticalsynchronizing signal, means at said receiver responsive to receivedvertical synchronizing signals to generate deflection signals, a counterat said receiver responsive to received different pulse groups toestablish dilerent digital manifestations substantially similar to thoseat said transmitter, a potential divider substantially similar to theone at said transmitter having a plurality of taps, means to apply thedeflection voltages generated at said receiver across said receiverpotential divider taps, switch means to select the deection signaloutput from different ones of said taps in a sequence determined by thedigital manifestations at said receiver, normally inoperative means topermit utilization of said deflection signals, means to establish a coindemand at said receiver for payment for a program, and means responsiveto payment of said coin demand to operate said normally inoperativemeans to permit utilization of said deection signals.

References Cited in the le of this patent UNITED STATES PATENTS2,472,774 Mayle u- June 7, 1949 2,656,411 Morris et al. Oct. 20, 19532,678,347 Clother May ll, 1954 2,757,226 Zworykin July 3l, 1956 FOREIGNPATENTS 15,789/34 Australia Ian. 19,-1934

